EP2385094B1 - Catalytic cracking method with recycling of an olefin cut taken upstream from the gas-separation section in order to maximise the production of propylene - Google Patents

Description

FIELD OF THE INVENTION

The present invention is in the field of catalytic cracking of petroleum fractions, more particularly so-called "heavy" cuts, and in the context of the evolution of catalytic cracking towards the co-production of light olefins, in particular propylene.

The main feedstock of a FCC unit (abbreviation for fluidized catalytic cracking) of heavy cuts is generally a hydrocarbon or a mixture of hydrocarbons containing essentially (ie at least 80%) molecules with a boiling point greater than 340 ° C. This main charge also contains limited quantities of metals (Ni + V), in concentration generally less than 50 ppm, preferably less than 20 ppm, and a hydrogen content in general of greater than 11% by weight, typically between 11.5. % and 14.5%, and preferably between 11.8% and 14% by weight.

The conradson carbon content (abbreviated as CCR) of the feed (defined by ASTM D 482) provides an evaluation of coke production during catalytic cracking. Depending on the conradson carbon content of the feed, the coke yield requires a specific sizing of the unit to satisfy the heat balance.

These heavy cuts may in particular come from atmospheric distillation, vacuum distillation, hydroconversion unit, coking unit, hydrotreatment unit or desalphating unit, but also have a biomass origin as per for example, vegetable oils or cellulose.

The heavy cuts constituting the main load of a catalytic cracking unit are hereafter called conventional heavy cuts and can be treated alone or as a mixture.

The main objective of the catalytic cracking unit of a refinery is the production of gasoline bases, ie cuts having a distillation range of between 35 ° C and 250 ° C.

Increasingly, this primary objective is accompanied by a new objective which is the production of light olefins, essentially ethylene and propylene.

Gasoline is produced by cracking the heavy load in the main reactor, called the main riser in the rest of the text, because of the elongated shape of this reactor and its upward flow mode. When the flow is down in the main reactor, it is called "downer".

The co-production of propylene is generally ensured by adding to the base catalytic system a shape-selective zeolite making it possible to improve the selectivity of LPG (abbreviation for liquefied petroleum gases) and gasoline, as well as by severing the operating conditions of the main riser. , mainly by increasing the temperature at the outlet of said reactor.

In order to achieve higher propylene yields, it is possible to recycle in an additional reactor, generally a secondary riser, a portion of the gasoline cut produced by the catalytic cracking unit, or an equivalent load such as oligomers of C6, C7 and C8 from the refinery.

The present invention describes a novel recycle stream for maximizing propylene yield.

It is known to a person skilled in the art that the recycle of the catalytic gasoline from the FCC into the reaction zone makes it possible to significantly increase the propylene yield by using appropriate operating conditions, ie a higher temperature. riser output and catalyst / load ratios (noted C / O) higher.

The advantage of the present invention is to take the new recycle, not after the separation section, but upstream of the latter, which makes it possible to overcome the costs of separation and benefit from a recycling to the properties ( chemical composition, especially olefin content) as good, or better (low aromatic content) than that of the petrol recycle according to the prior art.

The sampling point of the new recycle stream is located at the interstage of the wet gas compressor. This stream has a composition rich in C.sub.4 -C.sub.5 C.sub.6 to C.sub.8 compounds having a good olefinicity (ie olefin content), and it is practically free of aromatic compounds which, after recycle, tend to form mainly coke and penalize the thermal balance of the unit.

EXAMINATION OF THE PRIOR ART

It is known to a person skilled in the art that the recycle of the catalytic gasoline from the FCC into the reaction zone makes it possible to significantly increase the propylene yield by using appropriate operating conditions, ie a higher temperature. riser outlet and higher catalyst / load ratios (C / O). This recycle gasoline cracking can be carried out in the main riser of the unit or in a dedicated riser.

The prior art relating to catalytic cracking units with two risers, one conventional for obtaining gasoline, the other working under more stringent conditions for obtaining light olefins, is described in particular in the patent. FR 2.918.070

In this text we find the notions of main riser working on a heavy load, and secondary riser working at a high severity on a load partly formed by the recycling of gasoline produced at the main riser.

Moreover, the optimization independently of the operating conditions of two risers operating in parallel is described in the patent application. FR 2,932,495 .

The downer configuration is described in the patents EP 0 861 310 B1 , US6, 664, 171 B1 . The arrangement of an inner tube in a riser is described in the patent US7, 008, 527 B2

SUMMARY DESCRIPTION OF THE FIGURE

The figure 1 is a diagram of the process according to the invention in which it is shown the removal of the C4 C5 C6 olefinic cut at the interétage of the wet gas compressor and its recycling in the main riser of an FCC unit.

DESCRIPTTON SUMMARY OF THE INVENTION

The present invention is applicable to FCC units operating with a single reactor (in upflow or downflow), and to FCC units operating with two reactors.

In the remainder of the text, reference will be made to the main reactor rated (1) to designate the reactor oriented towards the conversion of the main charge, and secondary reactor noted (2) to designate the reactor dedicated to the production of propylene by cracking a cut recycle. Generally, when the FCC units operate with two reactors, one primary and one secondary, these reactors are upflow, but one unit that would use two downflow reactors remains within the scope of the present invention. It is also possible to consider the case of a unit with an upstream reactor and another downstream reactor.

Typically, the main riser operates with a catalyst to charge ratio of between 4 and 15, and preferably between 5 and 10, and with riser outlet temperatures. (TS) between 510 ° C and 580 ° C, and preferably between 520 ° C and 570 ° C.

The optimum conditions for the production of propylene in the secondary riser are obtained for outlet temperatures of said secondary riser of between 550 ° C. and 650 ° C., and preferably of between 580 ° C. and 610 ° C., contact times of 20 ° C. ms and 500 ms, preferably between 50 ms and 200 ms (ms = millisecond), and solid fluxes between 150 and 600 kg / s / m2.

The contact time is defined as the ratio of the volume of catalyst present in the reactor to the volumetric flow rate of fluid passing through the reactor to the conditions for carrying out the cracking reaction.

All of these conditions lead to operating the secondary riser catalyst to load ratios (noted C / O) between 8 and 35, and preferably between 10 and 25.

In the case of a main downer, it operates with a catalyst to charge ratio of between 5 and 40, and preferably between 10 and 30, and with downer outlet temperatures (denoted TS) of between 500 ° C. and 650 ° C. C, and preferably between 550 ° C and 630 ° C.

The optimum conditions for the production of propylene in a secondary downer are obtained for outlet temperatures of said secondary downer of between 550 ° C. and 650 ° C., and preferably between 580 ° C. and 630 ° C., contact times of between 20 ° C. and 650 ° C. ms and 800 ms, preferably between 50 ms and 500 ms (ms = millisecond). The present invention consists in recycling in the reaction section of an FCC unit a stream of C4, C5 and C6 olefinic compounds mainly. This recycle stream is taken at the inter-stage of the wet gas compressor (denoted CGH).

The advantage of the present invention is to take this recycle, not after the separation section, but upstream of the latter, which eliminates the costs of separation and benefit from a recycling properties (composition ) as good, or better (low amount of aromatics) than those of petrol recycle.

For simplification we call in the following text this flow, flow of interétage.

The flow from the inter stage of the wet gas compressor is largely composed of C4 and C5 olefins, typically in a proportion of 30% to 80%.

These C4 and C5 compounds have a high olefinicity, that is to say a high proportion of unsaturated compounds which can rise from 50% to 80% by weight for the C4 cut, and from 40% to 65% weight for the C5 cut. These unsaturated compounds of the interstage stream are subjected under particular operating conditions in an FCC riser to oligomerization reactions leading to the formation of compounds with larger carbon chain length. These oligomerized compounds in turn undergo catalytic cracking reactions leading to the formation of significant amounts of propylene.

The olefinic C4, C5 and C6 molecules contained in the interstage stream in question can be recycled either in the main reactor or in the secondary reactor when the FCC unit already comprises such a secondary reactor.

In the case of recycling in the main reactor, this recycle can be done either directly in mixture with the heavy load, or upstream of the injectors of said heavy load via dedicated injectors or a tube internal to riser.

In the case of recycling in the secondary riser, it may be either a dedicated riser, that is to say only treating the recycling in question, or a secondary riser already converting a light load such for example, some of the gasoline produced at the main riser, for the production of propylene.

In order to guarantee a stable flow of the interstage flow at the main or secondary riser (which could possibly vary due to fluctuations in the operation of the unit and the compressor), it is possible to associate the interstage flow with a supplement which can come from the downstream portion of the plant gas, preferably a catalytic gasoline. This booster can also be made up of any petroleum liquid or biomass compound with preferably an olefin content of greater than 20% and a carbon number of less than 12, in order to increase the production potential. of propylene.

This booster can be taken from the head of the FCC gasoline splitter at the bottom of the depropanizer. It can also come from an oligomerization unit or Pygas ex Steam Cracker.

DETAILED DESCRIPTION OF THE INVENTION

The following description is made by means of the figure 1 .

The figure 1 is a two-riser catalytic cracking unit (FCC), a main riser (1) and a secondary riser (2). The main riser (1) is supplied with regenerated catalyst from line (10), and the secondary riser is supplied with regenerated catalyst from line (9). The regeneration zone has two stages, a first stage (4) and a second stage (3) connected to the first stage by a catalyst transfer line (6).

The catalyst is transferred to the regeneration zone at the outlet of the stripping zone (8) via the transfer line (5).

The main riser (1) is fed by a conventional load (CH1) and the secondary riser (2) is fed by a lighter load (CH2).

The effluent stream (11) leaving the FCC unit is introduced into the separation column MC from which a noted head stream (12), one or more intermediate streams (14) and a bottom flow (13) are extracted. ). The intermediate streams (14) and the bottom stream (13) will not be described further to the extent that they do not interfere with the present invention.

• La phase liquide alimente pour une partie le reflux de la colonne (MC), et pour une autre partie (25) la séparation située en aval du compresseur de gaz humide (CGH) qui comporte deux étages (ET1, ET2).
• La phase gazeuse (15) issue du ballon (BS) est dirigée vers le premier étage du compresseur de gaz (ET1) après avoir été débarrassée des particules liquides qu'elle peut contenir dans le ballon séparateur (BS1).

We therefore resume the description at the head flow (12) which is condensed in the balloon (BS) and separated into two phases.

• The liquid phase feeds for some of the reflux of the column (MC), and for another part (25) the separation located downstream of the wet gas compressor (CGH) which has two stages (ET1, ET2).
• The gaseous phase (15) from the flask (BS) is directed to the first stage of the gas compressor (ET1) after being rid of the liquid particles that it can contain in the separator flask (BS1).

• un flux (19) qui est dirigé vers le second étage de compression (ET2) après être passé dans le ballon séparateur (BS3), devenant alors le flux 19a débarrassé des particules liquide. Le flux (19a) est compressé dans le deuxième étage de compression (ET2) pour délivrer le flux compressé (21) qui rejoint la section de récupération des gaz craqués (SRG),
• un flux (20) qui est dirigé vers la section de traitement des eaux usées (non représentée sur la figure 1),
• un flux (22) qui est recyclé vers le riser principal (1) ou le riser secondaire (2), ou partie vers le riser principal par le flux (25), et partie vers le riser secondaire par le flux (24) et qui constitue le flux d'interétage.

The compressed stream (16) from the first stage (ET1) is directed towards a second separator tank (BS2) from which three streams are extracted:

• a flow (19) which is directed to the second compression stage (ET2) after passing through the separator flask (BS3), thereby becoming the stream 19a freed of the liquid particles. The stream (19a) is compressed in the second compression stage (ET2) to deliver the compressed stream (21) which joins the cracked gas recovery section (SRG),
• a flow (20) which is directed to the wastewater treatment section (not shown on the figure 1 )
• a stream (22) which is recycled to the main riser (1) or the secondary riser (2), or part to the main riser by the stream (25), and part to the secondary riser by the stream (24) and which constitutes the interstage flow.

Since, as we clearly see on the figure 1 this flow (22) is well taken between the two compression stages ET1 and ET2 of the gas compressor, it is called interstage flow.

The invention can therefore be generally defined as a process for the production of propylene gasoline and co-production using a catalytic cracking unit. having at least one main reactor operating in a riser (so-called "riser") or downflow (called "downer") processing a conventional heavy load, and wherein the main reactor further processes a feed consisting of olefinic molecules predominantly in C4, C5 and C6 introduced in mixture with the heavy load or upstream of said heavy load, said olefinic charge being taken at the level of the interstage of the wet gas compressor (CGH) forming part of the gas treatment section ( SRG) associated with the FCC unit and constituting the interstage flow.

In a variant of the process for producing gasoline and coproduction of propylene according to the invention, the olefinic C4, C5 and C6 cut is introduced upstream of the main charge via an inner tube to said main riser opening from 1m to 0.5m before the level of the injectors of the main charge.

In general, if the main reactor operates in "downer" mode, it operates under the following operating conditions: reactor outlet temperature of between 580 ° C. and 630 ° C. and a C / O ratio of between 15 and 40, and preferably between 20 and 30, residence time between 0.1 and 1 s and preferably between 0.2 and 0.7 s.

In a variant of the propylene gasoline production and coproduction process according to the invention, said process uses a catalytic cracking unit having a main riser (1) treating a conventional filler (CH1) and a secondary riser (2). ) operating in parallel with the main riser (1) treating a filler (CH2) lighter than the heavy load (CH1) and operating at more severe operating conditions than those of the main riser, said secondary riser (2) treating the olefinic cut C4 C5 C6, represented by the flow (22) from the interstage of the wet gas compressor (CGH).

Still in the variant in which the process according to the invention uses a catalytic cracking unit using a main riser (1) and a secondary riser (2), the said secondary riser can mix the olefinic cut C4 C5 C6 (stream 22) from the interstage of the wet gas compressor (CGH), a gasoline cut and / or a C5, C6, C7 or C8 recycled oligomer, not shown in FIG. figure 1 .

Still in the variant in which the process according to the invention uses a catalytic cracking unit using a main riser (1) and a secondary riser (2), it is possible to add an additional flow to the interstage flow. (23) consisting of recycle gasoline so as to guarantee that the sum of the two flows, ie the interstage flow (22) plus the makeup flow (23), is constant within plus or minus 10%.

Still in the variant in which the process according to the invention uses a catalytic cracking unit using a main riser (1) and a secondary riser (2), the make-up stream (23) may consist of a hydrocarbon fraction oil or of biomass origin, having an olefin content greater than 20% by weight and containing compounds containing less than 12 carbon atoms.

Still in the variant in which the process according to the invention uses a catalytic cracking unit using a main riser (1) and a secondary riser (2), the make-up stream (23) can be taken either at the head of the FCC gasoline splitter, either at the bottom of the depropanizer forming part of the gas treatment section ("gas plant").

Still in the variant in which the process according to the invention uses a catalytic cracking unit using a main riser (1) and a secondary riser (2), the makeup flow (23) can come from a unit of oligomerization or Pygas ex Steam Cracker.

In the variant in which the process according to the invention uses a catalytic cracking unit using a main riser (1) and a secondary riser (2), the secondary riser (2) operates with a contact time of between 20 and 500 ms, preferably between 50 ms and 200 ms, and solid flows between 150 and 600 kg / s. m2.

In the variant in which the process according to the invention uses a catalytic cracking unit using a main riser (1) and a secondary riser (2), the C / O ratio of the main riser is between 6 and 14, preferably including between 7 and 12, and the C / O ratio of the secondary riser is between 8 and 35, preferably between 10 and 25.

In the variant in which the process according to the invention uses a catalytic cracking unit using a main riser (1) and a secondary riser (2), the outlet temperature of the main riser is between 510 ° C. and 580 ° C. preferably between 520 ° C. and 570 ° C., and the outlet temperature of the secondary riser is between 550 ° C. and 650 ° C., preferably between 580 ° C. and 610 ° C.

EXAMPLE

To illustrate the present invention, 5, 1, 2, 3, 4 and 5 examples were used.

Example 1

This first example is the basic case and corresponds to a mono-riser FCC unit with a capacity of 70000 BPSD, ie 500 m3 / hour, (BPSD abbreviation of barrels per day), treating a residual charge operating under maximum propylene conditions. that is to say with a catalytic system containing a shape-selective zeolite in order to improve the LPG selectivity on gasoline and operating under operating conditions that are more severe than the standard conditions of maximum gasoline operation.

The main characteristics of the load as well as the operating conditions considered are presented respectively in Table 1 and Table 2 below. <b> Table 1: Key Features of the Heavy Load </ b> Density 15/4 ° C .9305 Sulfur %weight 1,671 Nitrogen ppm weight 1222 Conradson Carbon %weight 4.36 Nickel ppm 12 Vanadium ppm 19 Viscosity (@ 50 ° C) cSt 84 Hydrogen %weight 12.33 Example 1 Unit capacity Bbl / d 70000 Charge rate t / h 431.6 Pressure output riser bar g 1.4 Output temperature riser ° C 550 Preheating temperature of the load ° C 260 Steam flow (MP) ton / h 29.6 Mass ratio catalyst flow over load flow 8

Under these conditions, the flow rates of the unit output products are given in Table 3 below. <b> Table 3: Flow rate of the products of Example 1 </ b> kg / h Example 1 Basic case Dry gases 22446 NH3 43 H2S 3913 H2 516 C1 6020 C2 4988 C2 = 6966 LPG 133171 C3 7568 C3 = 46612 C4 17243 C4 = 61748 LIQUID 236543 PI-160 113004 160-220 39302 PI-220 ° C 152306 220-360 54653 360 + 29584 Coke 37840 TOTAL 430000

Example 2

Example 2 corresponds to Example 1 with recycling of the interstage flow upstream of the main charge.

The operating conditions of the riser remain identical to those of Example 1.

Under these conditions, the flow of the interstage flow corresponds to 45 tons per hour and its composition is given in Table 4 below. <b> Table 4: Interstage flow composition Example 2 </ b> Composition of the interstage flow % weight C3 totals 4 C4 totals 20 C5 totals 30 C6-C8 46 C3 = in the total C3 86 C4 = in the total C4 60 C5 = in the total C5 51 Recycling rate, t / h 45

The rates of the unit output products with recycle are given and compared to those of the base case in Table 5 below. <b> Table 5: Comparison Example 1 and Example 2 </ b> kg / h Example1 Example 2 Delta Basic case Coprocessed interstage flow upstream of the heavy load % Dry gases 22446 23627 5.3 NH3 43 43 0.0 H2S 3913 3913 0.0 H2 516 571 10.6 C1 6020 6511 8.2 C2 4988 5243 5.1 C2 = 6966 7346 5.5 LPG 133171 134432 0.9 C3 7568 7927 4.7 C3 = 46612 48616 4.3 C4 17243 17855 3.5 C4 = 61748 60035 -2.8 LIQUID 236543 233089 -1.5 PI-160 113004 107500 -4.9 160-220 39302 40752 3.7 PI-220 ° C 152306 148252 -2.7 220-360 54653 55110 0.8 360 + 29584 29727 0.5 Coke 37840 38852 2.7 TOTAL 430000 430000 0.0

Under these conditions, the comparison of Tables 3 and 5 shows that the gain in propylene is more than 4 percent, which is obviously very significant on industrial flow.

A loss of C4 and C5 (through the PI-160 ° C cut) is obviously observed since these compounds were recycled and cracked.

An increase in dry gases and coke is also observed, but remains within the acceptable limits of the unit, especially from the point of view of the thermal balance.

The gain in ethylene which is also a recoverable product increases very significantly with an increase of more than 5%.

The recycle of the interstage flow (22) upstream of the main charge (CH1) therefore fully fulfills the objective of maximizing the production of propylene while avoiding the costs of separation compared with a conventional recycle. catalytic essence.

Example 3

Example 3 is similar to Example 2 except that this time the interstage flow is recycled to a secondary riser (2) dedicated and cracked under optimized operating conditions, namely a riser temperature of 590 ° C. and a contact time of 250ms. The flow rates of products obtained are presented and compared with those of Example 1 in Table 6. <b> Table 6: Comparison Example 1 and Example 3 </ b> kg / h Example1 Example 3 Delta Basic case Interstage stream cracked in a dedicated secondary riser % Dry gas 22446 24133 7.5 NH3 43 43 0.0 H2S 3913 3913 0.0 H2 516 594 15.2 C1 6020 6721 11.7 C2 4988 5352 7.3 C2 = 6966 7509 7.8 LPG 133171 134973 1.4 C3 7568 8080 6.8 C3 = 46612 49475 6.1 C4 17243 18117 5.1 C4 = 61748 59301 -4.0 LIQUID 236543 231609 -2.1 PI-160 113004 105141 -7.0 160-220 39302 41373 5.3 PI-220 ° C 152306 146514 -3.8 220-360 54653 55306 1.2 360+ 29584 29789 0.7. Coke 37840 39286 3.8 TOTAL 430000 430000 0.0

When the interstage flow is recycled to a dedicated riser (2) and subjected to optimized operating conditions, the propylene gain relative to the base case (Example 1) is more than 6%. It is therefore improved compared to the gain of 4% observed when this same recycle is cracked in the main riser upstream of the heavy load.

Under these conditions, ethylene also increases more widely with a gain of nearly 8% compared to the 5% of Example 2.

The increase in dry gases and coke is greater than in example 2, but this increase remains limited.

The recycle of the C4 and C5 rich cut in a dedicated riser thus allows greater propylene gains than when this load is cracked in a single riser upstream of the main load.

Example 4

The following example constitutes a second basic case and corresponds to an FCC unit comprising two risers, a main riser (1) fed with a residual charge (CH1), the same as for example 1, and a secondary riser ( 2) in which a part of the catalytic gasoline produced (CH2) is recycled and cracked under severe conditions. As in Example 1, the catalytic system comprises a shape-selective zeolite in order to optimize the operation of the unit in maximum propylene.

The operating conditions of Example 4 are described in Table 7. <b> Table 7: Operating conditions of Example 4 </ b> Case Example 4 Unit capacity Bbl / d 70,000 Main Riser Residual charge flow t / h 431.6 Pressure output riser bar g 1.4 Output temperature riser ° C 550 Preheating temperature of the load ° C 260 Steam flow (MP) t / h 29.6 Mass ratio catalyst flow over load flow 8 Secondary riser Catalytic gas recycle flow rate t / h 108 Output temperature riser ° C 590 Recycle temperature ° C 53 Steam flow (MP) t / h 3.3 Mass ratio catalyst flow over load flow 12

On this basis, the flow of unit output products are given in Table 8 <b> Table 8: Product Flow of Example 4 </ b> kg / h Example 4 Basic case dual riser recycle essence Dry gases 24940 NH3 43 H2S 3913 H2 602 C1 7095 C2 5504 C2 = 7783 LPG 142115 C3 8600 C3 = 51600 C4 18060 C4 = 63855 LIQUID 224632 PI-160 97782 160-220 41667 PI-220 ° C 139449 220-360 55556 360 + 29627 Coke 38313 TOTAL 430000

Example 5

Example 5 resumes the case of Example 4 but this time with a recycling of the interstage flow in the secondary riser mixed with gasoline from the FCC unit. Compared to Example 2, this recycle has changed in composition but the same recycling rate has been considered.

The composition of this recycle is provided in Table 9. <b> Table 9: Interstage flow composition Example 5 </ b> Composition of the interstage flow wt% C3 totals 6 C4 totals 20 C5 totals 56 C6-C8 18 C3 = in the total C3 84 C4 = in the total C4 80 C5 = in the total C5 51 Recycling rate t / h 45

The flow rates of the unit output products with recycle are given and compared with those of Example 4 in Table 10 <b> Table 10: Comparison Example 4 and Example 5 </ b> kg / h Example 4 Example 5 Delta Basic case dual riser recycle essence Dual riser recycles gasoline AND interstage flow at secondary riser Dry gases 24940 26911 7.9 NH3 43 43 0.0 H2S 3913 3913 0.0 H2 602 713 18.4 C1 7095 7921 11.6 C2 5504 5995 8.9 C2 = 7783 8326 7.0 LPG 142115 142487 0.3 C3 8600 9119 6.0 C3 = 51600 54550 5.7 C4 18060 18828 4.3 C4 = 63855 59989 -6.1 LIQUID 224632 220888 -1.7 PI-160 97782 92349 -5.6 160-220 41667 42873 2.9 PI-220 ° C 139449 135222 -3.0 220-360 55556 55959 0.7 360+ 29627 29707 0.3 Coke 38313 39714 3.7 TOTAL 430000 430000 0.0

The recycle of the interstage stream mixed with the gasoline from the FCC unit allows a sharp increase in propylene yield with an increase of nearly 6%. Ethylene progresses significantly with a gain of 7%. The yields of coke and dry gases increase but remain within acceptable limits. Ethylene rose by 7%, dry gases by almost 8% and coke by less than 4%. All of these examples show that in all cases, the recycling of the interstage flow (22) is at the main riser (1) or at the secondary riser (2), or partly at the main riser ( 1), and partly to the secondary riser (2), makes it possible to increase the yield of propylene very significantly.

Claims (12)

1. A process for the production of gasoline and the co-production of propylene employing a catalytic cracking unit having at least one principal reactor (1) functioning in upflow ("riser") mode or downflow ("downer") mode and treating a conventional heavy feed (CH1), and optionally a secondary riser (2) functioning under more severe conditions than the principal riser (1) and treating a lighter feed (CH2), in which process, in addition to the principal feed (CH1) and the optional lighter feed (CH2), a feed constituted mainly by C4, C5 and C6 olefinic molecules is treated, said olefinic feed being removed from the inter-stage of the wet gas compressor forming part of the gas treatment section (SPG) associated with the FCC unit and constituting the inter-stage stream (22).
2. A process for the production of gasoline and the co-production of propylene according to claim 1 in which, when the catalytic cracking unit has only one principal reactor (1), the olefinic C4, C5 and C6 feed corresponding to the inter-stage stream (22) is introduced as a mixture with the heavy feed (CH1).
3. A process for the production of gasoline and the co-production of propylene according to claim 1 in which, when the catalytic cracking unit has only one principal reactor (1), the olefinic C4, C5 and C6 feed corresponding to the inter-stage stream (22) is introduced upstream of the principal feed (CH1) via a pipe inside said principal riser (1) opening 1 m to 0.5 m before the level of the injectors for the principal feed (CH1).
4. A process for the production of gasoline and the co-production of propylene according to claim 1 in which, when the catalytic cracking unit further has a secondary riser (2) treating a lighter feed (CH2), and working under more severe operating conditions than those of the principal riser, the olefinic C4, C5 and C6 cut corresponding to the inter-stage stream (22) is introduced into the secondary riser (2).
5. A process for the production of gasoline and the co-production of propylene employing a catalytic cracking unit having a principal riser (1) and a secondary riser (2) according to claim 4, said secondary riser (2) treating the olefinic C4 C5 C6 cut corresponding to the inter-stage stream (22) and a recycled gasoline cut and/or a C5, C6, C7 or C8 oligomerizate cut as a mixture.
6. A process for the production of gasoline and the co-production of propylene employing a catalytic cracking unit according to claim 1, in which a makeup stream (23) constituted by recycled gasoline is added to the inter-stage stream (22) in order to ensure that the sum of the two streams, i.e. the inter-stage stream (22) plus the makeup stream (23), is constant to plus or minus 10%.
7. A process for the production of gasoline and the co-production of propylene employing a catalytic cracking unit according to claim 6, in which the makeup stream (23) is constituted by a hydrocarbon cut of oil or biomass origin having an olefins content of more than 20% by weight and containing compounds having less than 12 carbon atoms.
8. A process for the production of gasoline and the co-production of propylene employing a catalytic cracking unit according to claim 6, in which the makeup stream (23) is removed either from the head of the FCC gasoline splitter or from the bottom of the depropanizer forming part of the gas treatment section (SPG).
9. A process for the production of gasoline and the co-production of propylene employing a catalytic cracking unit according to claim 6, in which the makeup stream (23) derives from an oligomerization unit or from pygas, from a steam cracker.
10. A process for the production of gasoline and the co-production of propylene employing a catalytic cracking unit according to claim 4, in which the secondary riser (2) functions with a contact time in the range 20 to 500 ms, preferably in the range 50 ms to 200 ms, and with solid flow rates in the range 150 to 600 kg/s.m².
11. A process for the production of gasoline and the co-production of propylene employing a catalytic cracking unit according to claim 4, in which the C/O ratio of the principal riser (1) is in the range 6 to 14, preferably in the range 7 to 12, and the C/O ratio of the secondary riser (2) is in the range 8 to 35, preferably in the range 10 to 25.
12. A process for the production of gasoline and the co-production of propylene employing a catalytic cracking unit according to claim 4, in which the outlet temperature from the principal riser (1) is in the range 510°C to 580°C, preferably in the range 520°C to 570°C, and the outlet temperature from the secondary riser (2) is in the range 550°C to 650°C, preferably in the range 580°C to 610°C.

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